Method and apparatus for supporting positioning measurements

ABSTRACT

A method and apparatus for supporting positioning measurements. The methods include designating a reference cell, choosing a positioning signal, and, for inter-frequency measurements, determining which inter-frequency cell to measure and how to make such an inter-frequency positioning measurement.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. non-provisionalapplication Ser. No. 12/856,171, filed Aug. 13, 2010, which claims thebenefit of U.S. provisional application No. 61/233,655, filed Aug. 13,2009, each of which being incorporated by reference herein as if fullyset forth.

BACKGROUND

Support of wireless transmit/receive unit (WTRU)-based and WTRU-assistedobserved time difference of arrival (OTDOA) methods has been identifiedas one technique to improve upon achievable accuracy and speed forpositioning in a long term evolution (LTE) system.

For OTDOA methods, a WTRU observes signals of several neighbor cells,measures the observed time differences of arrival (for example, ascompared to its own serving cell), and reports these to the network. Inone method, the network then derives a positioning estimate based onfactors such as known deployment locations of the reported neighborsignals, known transmission time differences among various cells in thenetwork, and the like. This is referred to as WTRU-assisted positioning.Alternatively, the network provides the factors to the WTRU so that theWTRU computes its own position from the measurements using these factorsand the observed time differences of arrival measurements. This isreferred to as WTRU-based positioning.

WTRU time difference measurements may be defined based on one or morereference signals (RS) from the cells being measured. The RS may beeither Release 8 LTE Cell-Specific RS (CRS) and/or a newly designedPositioning RS (PRS). Either may be used individually or in combinationby the WTRU to derive the measured metrics. As a result, the WTRU mayneed to know which RS to use for the time difference measurements.

The time difference measurement that may be used for OTDOA calculationsmay be the Reference Signal Time Difference (RSTD). The RSTD may bedefined as the relative timing difference between a cell j and cell i,which may be defined as T_(SubframeRxj)−T_(SubframeRxi), whereT_(SubframeRxj) is the time when the WTRU receives the start of onesubframe from cell j and T_(SubframeRxi) is the time when the WTRUreceives the corresponding start of one subframe from cell i that isclosest in time to the subframe received from cell j. The referencepoint for the observed subframe time difference may be the antennaconnector of the WTRU. The RSTD measurement may be applicable tointra-frequency and inter-frequency cells. The WTRU, therefore, needs tosupport measurements made on neighbor cell carrier frequencies that aredifferent than the serving cell carrier frequency.

SUMMARY

A method and apparatus for supporting positioning measurements. Themethods include designating a reference cell, choosing a positioningsignal, and for inter-frequency measurements, determining whichinter-frequency cell to measure and how to make such an inter-frequencypositioning measurement.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1A is a system diagram of an example communications system in whichone or more disclosed embodiments may be implemented;

FIG. 1B is a system diagram of an example wireless transmit/receive unit(WTRU) that may be used within the communications system illustrated inFIG. 1A;

FIG. 1C is a system diagram of an example radio access network and anexample core network that may be used within the communications systemillustrated in FIG. 1A;

FIG. 2 shows an example location service support flow in EvolvedUniversal Mobile Telecommunications System (UMTS) Terrestrial RadioAccess Network (E-UTRAN);

FIG. 3 shows example positioning protocols in a long term evolution(LTE) positioning architecture; and

FIG. 4 shows an example flow diagram.

DETAILED DESCRIPTION

FIG. 1A is a diagram of an example communications system 100 in whichone or more disclosed embodiments may be implemented. The communicationssystem 100 may be a multiple access system that provides content, suchas voice, data, video, messaging, broadcast, etc., to multiple wirelessusers. The communications system 100 may enable multiple wireless usersto access such content through the sharing of system resources,including wireless bandwidth. For example, the communications system 100may employ one or more channel access methods, such as code divisionmultiple access (CDMA), time division multiple access (TDMA), frequencydivision multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrierFDMA (SC-FDMA), and the like.

As shown in FIG. 1A, the communications system 100 may include wirelesstransmit/receive units (WTRUs) 102 a, 102 b, 102 c, 102 d, a radioaccess network (RAN) 104, a core network 106, a public switchedtelephone network (PSTN) 108, the Internet 110, and other networks 112,though it will be appreciated that the disclosed embodiments contemplateany number of WTRUs, base stations, networks, and/or network elements.Each of the WTRUs 102 a, 102 b, 102 c, 102 d may be any type of deviceconfigured to operate and/or communicate in a wireless environment. Byway of example, the WTRUs 102 a, 102 b, 102 c, 102 d may be configuredto transmit and/or receive wireless signals and may include userequipment (UE), a mobile station, a fixed or mobile subscriber unit, apager, a cellular telephone, a personal digital assistant (PDA), asmartphone, a laptop, a netbook, a personal computer, a wireless sensor,consumer electronics, and the like.

The communications systems 100 may also include a base station 114 a anda base station 114 b. Each of the base stations 114 a, 114 b may be anytype of device configured to wirelessly interface with at least one ofthe WTRUs 102 a, 102 b, 102 c, 102 d to facilitate access to one or morecommunication networks, such as the core network 106, the Internet 110,and/or the networks 112. By way of example, the base stations 114 a, 114b may be a base transceiver station (BTS), a Node-B, an eNode B, a HomeNode B, a Home eNode B, a site controller, an access point (AP), awireless router, and the like. While the base stations 114 a, 114 b areeach depicted as a single element, it will be appreciated that the basestations 114 a, 114 b may include any number of interconnected basestations and/or network elements.

The base station 114 a may be part of the RAN 104, which may alsoinclude other base stations and/or network elements (not shown), such asa base station controller (BSC), a radio network controller (RNC), relaynodes, etc. The base station 114 a and/or the base station 114 b may beconfigured to transmit and/or receive wireless signals within aparticular geographic region, which may be referred to as a cell (notshown). The cell may further be divided into cell sectors. For example,the cell associated with the base station 114 a may be divided intothree sectors. Thus, in one embodiment, the base station 114 a mayinclude three transceivers, i.e., one for each sector of the cell. Inanother embodiment, the base station 114 a may employ multiple-inputmultiple output (MIMO) technology and, therefore, may utilize multipletransceivers for each sector of the cell.

The base stations 114 a, 114 b may communicate with one or more of theWTRUs 102 a, 102 b, 102 c, 102 d over an air interface 116, which may beany suitable wireless communication link (e.g., radio frequency (RF),microwave, infrared (IR), ultraviolet (UV), visible light, etc.). Theair interface 116 may be established using any suitable radio accesstechnology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 104 and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Universal MobileTelecommunications System (UMTS) Terrestrial Radio Access (UTRA), whichmay establish the air interface 116 using wideband CDMA (WCDMA). WCDMAmay include communication protocols such as High-Speed Packet Access(HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed DownlinkPacket Access (HSDPA) and/or High-Speed Uplink Packet Access (HSUPA).

In another embodiment, the base station 114 a and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Evolved UMTSTerrestrial Radio Access (E-UTRA), which may establish the air interface116 using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A)technology.

In other embodiments, the base station 114 a and the WTRUs 102 a, 102 b,102 c may implement radio technologies such as IEEE 802.16 (i.e.,Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000,CDMA2000 1X, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), InterimStandard 95 (IS-95), Interim Standard 856 (IS-856), Global System forMobile communications (GSM), Enhanced Data rates for GSM Evolution(EDGE), GSM EDGE (GERAN), and the like.

The base station 114 b in FIG. 1A may be a wireless router, Home Node B,Home eNode B, or access point, for example, and may utilize any suitableRAT for facilitating wireless connectivity in a localized area, such asa place of business, a home, a vehicle, a campus, and the like. In oneembodiment, the base station 114 b and the WTRUs 102 c, 102 d mayimplement a radio technology such as IEEE 802.11 to establish a wirelesslocal area network (WLAN). In another embodiment, the base station 114 band the WTRUs 102 c, 102 d may implement a radio technology such as IEEE802.15 to establish a wireless personal area network (WPAN). In yetanother embodiment, the base station 114 b and the WTRUs 102 c, 102 dmay utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE,LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG. 1A,the base station 114 b may have a direct connection to the Internet 110.Thus, the base station 114 b may not be required to access the Internet110 via the core network 106.

The RAN 104 may be in communication with the core network 106, which maybe any type of network configured to provide voice, data, applications,and/or voice over internet protocol (VoIP) services to one or more ofthe WTRUs 102 a, 102 b, 102 c, 102 d. For example, the core network 106may provide call control, billing services, mobile location-basedservices, pre-paid calling, Internet connectivity, video distribution,etc., and/or perform high-level security functions, such as userauthentication. Although not shown in FIG. 1A, it will be appreciatedthat the RAN 104 and/or the core network 106 may be in direct orindirect communication with other RANs that employ the same RAT as theRAN 104 or a different RAT. For example, in addition to being connectedto the RAN 104, which may be utilizing an E-UTRA radio technology, thecore network 106 may also be in communication with another RAN (notshown) employing a GSM radio technology.

The core network 106 may also serve as a gateway for the WTRUs 102 a,102 b, 102 c, 102 d to access the PSTN 108, the Internet 110, and/orother networks 112. The PSTN 108 may include circuit-switched telephonenetworks that provide plain old telephone service (POTS). The Internet110 may include a global system of interconnected computer networks anddevices that use common communication protocols, such as thetransmission control protocol (TCP), user datagram protocol (UDP) andthe internet protocol (IP) in the TCP/IP internet protocol suite. Thenetworks 112 may include wired or wireless communications networks ownedand/or operated by other service providers. For example, the networks112 may include another core network connected to one or more RANs,which may employ the same RAT as the RAN 104 or a different RAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities, i.e., theWTRUs 102 a, 102 b, 102 c, 102 d may include multiple transceivers forcommunicating with different wireless networks over different wirelesslinks. For example, the WTRU 102 c shown in FIG. 1A may be configured tocommunicate with the base station 114 a, which may employ acellular-based radio technology, and with the base station 114 b, whichmay employ an IEEE 802 radio technology.

FIG. 1B is a system diagram of an example WTRU 102. As shown in FIG. 1B,the WTRU 102 may include a processor 118, a transceiver 120, atransmit/receive element 122, a speaker/microphone 124, a keypad 126, adisplay/touchpad 128, non-removable memory 130, removable memory 132, apower source 134, a global positioning system (GPS) chipset 136, andother peripherals 138. It will be appreciated that the WTRU 102 mayinclude any sub-combination of the foregoing elements while remainingconsistent with an embodiment.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Array (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 118 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 102 to operate in a wirelessenvironment. The processor 118 may be coupled to the transceiver 120,which may be coupled to the transmit/receive element 122. While FIG. 1Bdepicts the processor 118 and the transceiver 120 as separatecomponents, it will be appreciated that the processor 118 and thetransceiver 120 may be integrated together in an electronic package orchip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, thetransmit/receive element 122 may be an antenna configured to transmitand/or receive RF signals. In another embodiment, the transmit/receiveelement 122 may be an emitter/detector configured to transmit and/orreceive IR, UV, or visible light signals, for example. In yet anotherembodiment, the transmit/receive element 122 may be configured totransmit and receive both RF and light signals. It will be appreciatedthat the transmit/receive element 122 may be configured to transmitand/or receive any combination of wireless signals.

In addition, although the transmit/receive element 122 is depicted inFIG. 1B as a single element, the WTRU 102 may include any number oftransmit/receive elements 122. More specifically, the WTRU 102 mayemploy MIMO technology. Thus, in one embodiment, the WTRU 102 mayinclude two or more transmit/receive elements 122 (e.g., multipleantennas) for transmitting and receiving wireless signals over the airinterface 116.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as UTRA, E-UTRA and IEEE802.11, for example.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad 128 (e.g., a liquid crystal display (LCD) displayunit or organic light-emitting diode (OLED) display unit). The processor118 may also output user data to the speaker/microphone 124, the keypad126, and/or the display/touchpad 128. In addition, the processor 118 mayaccess information from, and store data in, any type of suitable memory,such as the non-removable memory 130 and/or the removable memory 132.The non-removable memory 130 may include random-access memory (RAM),read-only memory (ROM), a hard disk, or any other type of memory storagedevice. The removable memory 132 may include a subscriber identitymodule (SIM) card, a memory stick, a secure digital (SD) memory card,and the like. In other embodiments, the processor 118 may accessinformation from, and store data in, memory that is not physicallylocated on the WTRU 102, such as on a server or a home computer (notshown).

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries (e.g., nickel-cadmium (NiCd),nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion),etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information (e.g., longitude andlatitude) regarding the current location of the WTRU 102. In additionto, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 116 from abase station (e.g., base stations 114 a, 114 b) and/or determine itslocation based on the timing of the signals being received from two ormore nearby base stations. It will be appreciated that the WTRU 102 mayacquire location information by way of any suitablelocation-determination method while remaining consistent with anembodiment.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 138 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth® module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, and the like.

FIG. 1C is a system diagram of the RAN 104 and the core network 106according to an embodiment. As noted above, the RAN 104 may employ anE-UTRA radio technology to communicate with the WTRUs 102 a, 102 b, 102c over the air interface 116. The RAN 104 may also be in communicationwith the core network 106.

The RAN 104 may include eNode-Bs 140 a, 140 b, 140 c, though it will beappreciated that the RAN 104 may include any number of eNode-Bs whileremaining consistent with an embodiment. The eNode-Bs 140 a, 140 b, 140c may each include one or more transceivers for communicating with theWTRUs 102 a, 102 b, 102 c over the air interface 116. In one embodiment,the eNode-Bs 140 a, 140 b, 140 c may implement MIMO technology. Thus,the eNode-B 140 a, for example, may use multiple antennas to transmitwireless signals to, and receive wireless signals from, the WTRU 102 a.

Each of the eNode-Bs 140 a, 140 b, 140 c may be associated with aparticular cell (not shown) and may be configured to handle radioresource management decisions, handover decisions, scheduling of usersin the uplink and/or downlink, and the like. As shown in FIG. 1C, theeNode-Bs 140 a, 140 b, 140 c may communicate with one another over an X2interface.

The core network 106 shown in FIG. 1C may include a mobility managementgateway (MME) 142, a serving gateway 144, and a packet data network(PDN) gateway 146. While each of the foregoing elements are depicted aspart of the core network 106, it will be appreciated that any one ofthese elements may be owned and/or operated by an entity other than thecore network operator.

The MME 142 may be connected to each of the eNode-Bs 142 a, 142 b, 142 cin the RAN 104 via an S1 interface and may serve as a control node. Forexample, the MME 142 may be responsible for authenticating users of theWTRUs 102 a, 102 b, 102 c, bearer activation/deactivation, selecting aparticular serving gateway during an initial attach of the WTRUs 102 a,102 b, 102 c, and the like. The MME 142 may also provide a control planefunction for switching between the RAN 104 and other RANs (not shown)that employ other radio technologies, such as GSM or WCDMA.

The serving gateway 144 may be connected to each of the eNode Bs 140 a,140 b, 140 c in the RAN 104 via the S1 interface. The serving gateway144 may generally route and forward user data packets to/from the WTRUs102 a, 102 b, 102 c. The serving gateway 144 may also perform otherfunctions, such as anchoring user planes during inter-eNode B handovers,triggering paging when downlink data is available for the WTRUs 102 a,102 b, 102 c, managing and storing contexts of the WTRUs 102 a, 102 b,102 c, and the like.

The serving gateway 144 may also be connected to the PDN gateway 146,which may provide the WTRUs 102 a, 102 b, 102 c with access topacket-switched networks, such as the Internet 110, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and IP-enableddevices.

The MME 142 or serving gateway 144 may interface with an evolved servingmobile location center (E-SMLC) 150 for at least control planepositioning support and for sending location information to or receivinglocation information from the WTRUs 102 a, 102 b, 102 c.

The core network 106 may facilitate communications with other networks.For example, the core network 106 may provide the WTRUs 102 a, 102 b,102 c with access to circuit-switched networks, such as the PSTN 108, tofacilitate communications between the WTRUs 102 a, 102 b, 102 c andtraditional land-line communications devices. For example, the corenetwork 106 may include, or may communicate with, an IP gateway (e.g.,an IP multimedia subsystem (IMS) server) that serves as an interfacebetween the core network 106 and the PSTN 108. In addition, the corenetwork 106 may provide the WTRUs 102 a, 102 b, 102 c with access to thenetworks 112, which may include other wired or wireless networks thatare owned and/or operated by other service providers.

Focusing on the control plane only, location service support flow isshown with respect to FIG. 2. A WTRU 200 or an eNB 210 may request somelocation service (e.g., positioning or delivery of assistance data) fromthe serving MME 220 at the non-access stratum (NAS) level (1 a).Alternatively, an entity in the evolved packet core (EPC) 240 (e.g.,Gateway Mobile Location Centre (GMLC)) may request some location service(e.g. positioning) for a target WTRU to the serving MME 220 (1 b).Alternatively, the serving MME 220 for a target WTRU 200 may determinethe need for some location service (e.g. to locate the WTRU 200 for anemergency call) (1 c).

The MME may then transfer the location service request to an E-SMLC 230(2). The E-SMLC 230 may then instigate location procedures with theserving eNB 210 for the WTRU 200, e.g., to obtain positioningmeasurements or assistance data (3 a). In addition or instead of step 3a, the E-SMLC 230 may instigate location procedures with the WTRU 200,(e.g., to obtain a location estimate or positioning measurements or totransfer location assistance data to the WTRU 200 (3 b)). The E-SMLC 230may then provide a location service response to the MME 220 and includeany needed results, e.g., a success or failure indication and, ifrequested and obtained, a location estimate for the WTRU (4).

If step 1 a was performed, the MME 220 may return a location serviceresponse to the WTRU 200 (or the eNB 210) and include any neededresults, (e.g., a location estimate for the WTRU 200 (5 a)). If step 1 bwas performed, the MME 220 may return a location service response to theEPC entity in step 1 b and include any needed results, (e.g., a locationestimate for the WTRU (5 b)). If step 1 c occurred, the MME 220 may usethe location service response received in step 4 to assist the servicethat triggered this in step 1 c, (e.g., may provide a location estimateassociated with an emergency call to a GMLC) (5 c).

FIG. 3 shows the two protocols that may be used for support ofpositioning: LTE positioning protocol (LPP) and LTE positioning protocola (LPPa). The LPP protocol is a point-to-point protocol between theE-SMLC 300 and the WTRU 330. The LPP passes through the MME 310 and eNB320 to the WTRU. The LPPa protocol may be used for transfer ofpositioning related information (e.g., PRS scheduling information)between the eNB 320 and the E-SMLC 300.

For OTDOA methods, a WTRU observes signals of several neighbor cells,measures the observed time differences of arrival (for example, ascompared to its own serving cell), and reports these to the network. Inone method, the network then derives a positioning estimate based onfactors such as known deployment locations of the reported neighborsignals, known transmission time differences among various cells in thenetwork, and the like. This is referred to as WTRU-assisted positioning.Alternatively, the network provides the factors to the WTRU so that theWTRU computes its own position from the measurements using these factorsand the observed time differences of arrival measurements. This isreferred to as WTRU-based positioning.

WTRU time difference measurements may be defined based on one or morereference signals (RS) from cells being measured. The RS may be eitherRelease 8 LTE Cell-Specific RS (CRS) and/or a newly designed PositioningRS (PRS). Either may be used individually or in combination by the WTRUto derive the measured metrics.

The PRS to be used by the WTRU for positioning purposes may be containedin either normal subframe(s), or in Multi-Media Broadcast over a SingleFrequency Network (MBSFN)-reserved subframes. The PRS bandwidth may beconfigurable, e.g., up to the system bandwidth in a subframe.

Without loss of generality and for illustration purposes, more than onepositioning subframe allocation may be needed by the WTRU to accumulateenough energy to get to one measurement sample for one or more specificneighbors. For example, 1, 2, 4 or 6 consecutive positioning subframesmay be needed to derive one sample. Furthermore, positioning subframesmay typically occur in certain periodicities, (e.g. 16, 32, 64, or 128radio frames, and positioning occasions may be semi-staticallyconfigured and coordinated among neighboring eNodeBs).

MBSFN-reserved subframes, when used as positioning subframes, may havethe same PRS pattern as normal subframes. Specifically, the same PRSpattern may be used in all PRBs used for positioning in frequencydimension in one subframe. The PRS pattern(s) similar to the CRS inRelease 8 LTE may be generated as a function of the Physical Cell ID(PCI) as one input parameter.

Assistance data may be provided to the WTRU through higher layersignaling such as radio resource control (RRC) or LPP signaling.

The time difference measurement that may be used for OTDOA calculationsmay be the Reference Signal Time Difference (RSTD). The RSTD may bedefined as the relative timing difference between a cell j and cell i,which may be defined as T_(SubframeRxj)−T_(SubframeRxi), whereT_(SubframeRxj) is the time when the WTRU receives the start of onesubframe from cell j and T_(SubframeRxi) is the time when the WTRUreceives the corresponding start of one subframe from cell i that isclosest in time to the subframe received from cell j. The referencepoint for the observed subframe time difference may be the antennaconnector of the WTRU. The RSTD measurement may be applicable tointra-frequency cell measurements and inter-frequency cell measurements.

When making inter-frequency measurements, the WTRU may need to tune itsreceiver to the appropriate downlink (DL) carrier frequency and maytherefore not be able to receive on the serving cell DL frequency. Inaddition, many common WTRU RF implementations may use frequencysynthesizers where a single oscillator may be employed to derive both DLreceive (Rx) and uplink (UL) transmit (Tx) frequencies. This radiofrequency (RF) architecture may be facilitated by the use of commonDL-UL frequency duplex distances in 3G and LTE technology. Therefore,when the WTRU tunes its DL Rx frequency for measurement purposes to adifferent DL frequency channel than the one employed by its own servingcell, the WTRU may not be able to simultaneously transmit on the UL Txfrequency channel in use in that serving cell either. In addition, someDL frequency channels in certain 3G or LTE frequency bands may be tooclose to UL frequency channels of other 3G or LTE bands, such that a DLmeasurement may not be reliably performed without self-interference fromconcurrent UL transmissions by the WTRU even where the WTRU RFarchitecture may support such separate tuning of DL Rx and UL Txfrequencies.

Although the methods described herein are shown in terms of OTDOA andRSTD, the methods are applicable to any positioning measurements andpositioning methods. Moreover, although the methods described herein aredescribed in particular combinations, each method and/or part of eachmethod may be used alone or in combination with other methods or partsof other methods.

Methods are described herein for choosing between a CRS or PRS. In onemethod, the WTRU may determine whether to use CRS or PRS for positioningmeasurements based on the existence of a PRS. The WTRU may know of theexistence and subframe allocation of the PRS in the serving cell basedon high layer signaling. The information may be broadcast or sent viadedicated signaling.

For example, if PRS exists in the serving cell, the WTRU may use it fordetermining serving cell timing for use in positioning measurements, forexample RSTD. In another example, the WTRU may use PRS for determiningtiming relative to the serving cell, such as RSTD, of anyintra-frequency cells that transmit PRS in the same subframes as theserving cell, (i.e., the WTRU looks for PRS of other cells in the samesubframe as the PRS of the serving cell and determines their relativetiming to the serving cell, for example, RSTD). In a further example,the WTRU may use the PRS for determining timing relative to the servingcell, such as RSTD, of any intra-frequency cells that transmit PRS insubframes that are different from those containing PRS of the servingcell, but are known to the WTRU, (e.g., in the case of asynchronous PRStransmission where the WTRU is told, for example, the system framenumber (SFN) offset between the neighbor cell and serving celltransmissions).

In another method, if the serving cell does not support PRS, then theWTRU may use CRS for both the serving cell and each other cell that maybe used for positioning measurements, and for determining the relativetime difference between each cell and the serving cell, such as for RSTDin support of OTDOA.

In another method, if a cell to be measured does not support PRS, thenthe WTRU may make the RSTD measurement for that cell and the servingcell based on CRS measurements for both cells.

In another method, the WTRU may make an RSTD measurement using PRS forone cell and CRS for the other cell.

In another method, explicit higher layer signaling may be used to tellthe WTRU whether to use CRS or PRS. For example, the E-SMLC may signalthe WTRU via LPP signaling whether PRS should be used for the servingcell, and for which other cells. The default may be to use CRS, i.e., ifthe WTRU is not told to use PRS, then the WTRU may use CRS.

In another method, if a cell, serving or other, supports PRS, then theWTRU may use PRS for the positioning measurement for that cell. If acell, serving or other, does not support PRS, then the WTRU may use CRSfor the positioning measurement for that cell.

In another method, higher layer signaling may be used to tell the WTRUwhether or not each cell to be measured supports PRS. If the WTRU is nottold that a cell to be measured supports PRS, then the WTRU may assumethat it does not support PRS.

In another method, higher layer signaling may be used to tell the WTRUwhether or not each cell to be measured is synchronized in itstransmission of PRS with the serving cell. The higher layer signalingmay allow for the possibility of informing the WTRU that all cells (orall cells to be measured) are synchronized in their transmission of thePRS with the serving cell. This may be done using, for example, a singlebit.

In another method, if PRS is to be used for the measurement, but the PRSmeasurement is of poor quality, then the WTRU may attempt to use CRS .If both PRS and CRS are of poor quality, the WTRU may discard the RSTDmeasurement.

In another method, threshold parameters may be provided to the WTRU bythe network for use in determining whether the RS measurements are ofsufficient quality for acceptable RSTD measurements.

In another method, the WTRU may use either CRS or PRS measurementsdepending on which provides the better quality. For each of the servingcell and other cell, the WTRU may use CRS or PRS based on the individualquality. Alternatively, for both the serving cell and other cell, theWTRU may use CRS or PRS (same for both) based on the individualqualities and/or the combined quality.

Described herein are methods for designating and using reference cells.

In an example method for designating a reference cell, the network maytell the WTRU which cell is the reference cell for positioningmeasurements. The reference cell may or may not be the serving cell.Allowing a reference cell to be a cell other than the serving cell mayprovide benefits such as the ability to continue positioning throughhandover. That is, the WTRU may continue positioning measurements andmeasurement reporting after handover without changes to reference orneighbor cells or the need for new assistance data.

In one embodiment, if the WTRU is not told which cell is the referencecell, then the default reference cell may be the serving cell.

In an example method of when the reference cell is not the serving cell,the existence and subframe allocation of the PRS may be provided to theWTRU via high layer signaling.

If the WTRU is not told of the existence of PRS and/or what the subframeallocation is for the PRS in the reference cell, then the default may bethe same as the serving cell. That is, if the WTRU is not told of theexistence of PRS in the reference cell, then the existence of PRS in thereference cell is the same as the existence of PRS in the serving cell.If the WTRU is not told the subframe allocation of PRS in the referencecell, then the subframe allocation in the reference cell is the same asthe subframe allocation of PRS in the serving cell.

Alternatively, if the WTRU is not told of the existence of PRS in thereference cell, then the WTRU understands that PRS is not supported inthe reference cell. If the WTRU is told that PRS exists in the referencecell but is not told the subframe allocation of PRS in the referencecell, then the subframe allocation in the reference cell is the same asthe subframe allocation of PRS in the serving cell.

Alternatively, if the WTRU is not told of the existence of PRS in thereference cell, then the WTRU understands that PRS is not supported inthe reference cell. If the WTRU is told that PRS exists in the referencecell but is not told the subframe allocation of PRS in the referencecell, then this may be seen as an error and the WTRU may act as if PRSis not configured in the reference cell.

In an example method of when PRS exists in the reference cell, the WTRUuses it for determining reference cell timing for use in positioningmeasurements, for example RSTD.

In another example method, if PRS exists in the reference cell and thereference cell is an intra-frequency cell, the WTRU may use PRS fordetermining timing relative to the reference cell, for example RSTD, ofany intra-frequency cells that transmit PRS in the same subframes as thereference cell, i.e., the WTRU may look for PRS of other cells in thesame subframe as PRS of the reference cell and determine their relativetiming to the reference cell, for example RSTD.

In another example method, if PRS exists in the reference cell and thereference cell is an intra-frequency cell, the WTRU may use it fordetermining timing relative to the serving cell, for example RSTD, ofany intra-frequency cells that transmit PRS in subframes that aredifferent from those containing PRS of the reference cell, but are knownto the WTRU. For example, as in the case of asynchronous PRStransmission where the WTRU may be told the SFN offset between theneighbor cell and reference cell transmissions (or the SFN offsetbetween the neighbor cell and the serving cell and the reference celland the serving cell so that it can derive the SFN offset between theneighbor cell and reference cell transmissions).

In an example method of when the reference cell does not support PRS,then the WTRU may use CRS for both the reference cell and each othercell used for positioning measurements for determining the relative timedifference between each cell and the reference cell, for example forRSTD in support of OTDOA.

In an example method of when a cell to be measured does not support PRS,then the WTRU measurement of RSTD for that cell may be based on CRSmeasurements for both that cell and the reference cell.

In an example method, explicit higher layer signaling may be used totell the WTRU whether to use CRS or PRS. For example, the E-SMLC maysignal the WTRU via LPP signaling whether PRS should be used for thereference cell, and for which of the non-reference cells. In the case ofexplicit signaling, the default may be to use CRS, i.e., if the WTRU isnot told to use PRS, then the WTRU may use CRS.

In an example method of when a cell, reference or other, supports PRS,then the WTRU may use PRS for the measurement for that cell. If a cell,reference or other, does not support PRS, then the WTRU may use CRS forthe measurement for that cell.

In an example method, higher layer signaling may be used to tell theWTRU whether or not each non-reference cell to be measured supports PRS.If the WTRU is not told that a non-reference cell to be measuredsupports PRS, then the WTRU understands that it does not support PRS.

In another example method, higher layer signaling may be used to tellthe WTRU whether or not each non-reference cell to be measured issynchronized in its transmission of PRS with the reference cell. Thehigher layer signaling may allow for the possibility of informing theWTRU that all non-reference cells (or all non-reference cells to bemeasured) are synchronized in their transmission of the PRS with thereference cell, for example using a single bit.

In another example method, the WTRU may use either CRS or PRSmeasurements depending on which provides the better quality. For each ofthe reference cell and non-reference cell, the WTRU may use CRS or PRSbased on the individual quality. Alternatively, for both the referencecell and neighbor cell, the WTRU may use CRS or PRS (same for both)based on the individual qualities and/or the combined quality.

Described herein are methods for performing inter-frequency RSTDmeasurements.

In an example method, for inter-frequency neighbor cells to be used forpositioning measurements, for example for OTDOA measurements, thecarrier frequency(ies) of the cell(s) may be provided to the WTRU by thenetwork.

In an embodiment of the example method, for inter-frequency neighborcells to be used for positioning measurements, for example for OTDOAmeasurements, the carrier frequency(ies) of the cell(s) may be providedto the WTRU by the network as part of assistance data. Assistance datamessages containing such inter-frequency cells indicated for positioningmeasurements by the WTRU may be realized through RRC or LPP signalingexchanges with one or more network nodes, such as eNB(s) or E-SMLC(s),with the WTRU. Alternatively, other protocol messages may be used, suchas for example, medium access control (MAC) control packet data units(PDU(s)) or equivalent messages.

In one embodiment, the evolved absolute radio frequency channel number(EARFCN) of the inter-frequency cell(s) indicated for positioningmeasurements may be provided in the assistance data.

In another embodiment, the carrier frequency(ies) of the inter-frequencycell(s) indicated for positioning measurements may be provided to theWTRU by the E-SMLC via LPP signaling.

In another method, the WTRU may determine which carrier frequenciesand/or inter-frequency cells to measure for positioning purposes, forexample for OTDOA measurements, based on existing carrier frequencylist(s) and/or inter-frequency neighbor cell list(s) already provided tothe WTRU by one or more network nodes, such as the eNodeB(s), formobility handling purpose and the like.

In one embodiment, either all or some of the carrier frequencies and/orinter-frequency cells indicated for other measurement purposes such asmobility handling may qualify as inter-frequency measurement candidatesfor positioning purposes for the WTRU.

In another embodiment, carrier frequencies and/or inter-frequency cellsotherwise discarded by the WTRU for measurement purposes (such as formobility handling) due to specific measurement rules in that context,may be considered by the WTRU as valid measurement candidates forpositioning purposes.

In another embodiment, the WTRU may determine which carrier frequenciesand/or inter-frequency cells to measure for positioning purposes basedon the carrier frequencies and/or inter-frequency cells provided to theWTRU in the InterFreqCarrierFreqList and/or the InterFreqNeighListprovided through RRC signaling.

In another embodiment, the WTRU may determine which frequency channelsand/or inter-frequency cells to evaluate for positioning purposes basedon existing measurement lists and may not preclude cells in theInterFreqBlackCellList from measurements to be used for positioning.

In another embodiment, the WTRU may exclude from inter-frequencymeasurements for positioning any carrier frequencies and/or candidatecells that are not provided in the inter-frequency neighbor carrierand/or cell list(s) provided by the eNB. For example, in the case wherethe E-SMLC provides carrier frequencies of the inter-frequency cells tobe measured for positioning purposes, if there are frequencies in thatlist that are not also included in the inter-frequency neighbor carrierand/or cell list(s) provided by the eNB, the WTRU may exclude thosefrequencies from positioning measurements.

In another embodiment, in the case where the E-SMLC provides a list ofinter-frequency cells to be measured for positioning purposes, if thereare inter-frequency cells in that list that are not also included in theinter-frequency neighbor cell list(s) provided by the eNB, the WTRU mayexclude those cells (the ones not on the inter-frequency neighbor celllist(s) provided by the eNB) from positioning measurements.

In an example method, the cells the WTRU measures for positioningpurposes may be limited to those whose strength or reception quality isgood enough or deemed reliable enough as determined by othermeasurements.

In one embodiment, those other measurements used in this determinationmay be reference signal received power (RSRP) and/or reference signalreceived quality (RSRQ).

In another embodiment, if the RSRP and/or RSRQ measurements do notexceed specified thresholds, the WTRU may exclude the related cell(s)and/or the related frequency(s) from positioning measurements.

In another embodiment, the threshold parameters may be provided to theWTRU by the network for use in determining if applicable signal strengthor signal quality levels, for example based on RSRP and/or RSRQmeasurements, are good enough to consider specific cells and/or specificcarrier frequencies for positioning measurements.

In another embodiment, the WTRU may configure applicable signal strengthor signal quality levels based on its own measurements and withoutintervention of the network.

In another embodiment, different signal strength or reception qualitythresholds may be configured in the WTRU for different measurementobjects. For example, a first signal quality threshold may apply to afirst frequency channel used for positioning purposes, and a second,possibly different signal quality threshold may apply to a secondfrequency channel used for positioning purposes, and so on.

In an example method, the serving eNB may inform the E-SMLC of thestrength and/or quality of measurements reported by the WTRU to enablethe E-SMLC to determine which cells and/or which frequencies the WTRUshould measure subsequently.

In an embodiment, the eNB may inform the E-SMLC of the WTRU'smeasurements of RSRP and/or RSRQ. This information may be signaled usingLPPa signaling.

In an example method, when a WTRU may be told by the E-SMLC to performinter-frequency positioning measurements, the E-SMLC may also inform theserving eNB for that WTRU. In a further example, the E-SMLC may informthe eNB using LPPa signaling. The E-SMLC may also inform the eNB thatinter-frequency positioning measurements may be required of the specificWTRU and may optionally include the carrier frequencies and/or the cellIDs of the cell or cells to be measured. In yet a further example, theeNB may also configure measurement gaps in the WTRU as needed to supportthese inter-frequency measurements.

In an example method, the serving eNB may inform the E-SMLC of thecarrier frequencies of the cells for which the WTRU may be reportingmeasurements. For example, this may include the carrier frequencies ofthe cells for which the WTRU may be reporting RSRP and/or RSRQ. TheE-SMLC is thus aware of the carrier frequencies the WTRU is alreadyhearing and measuring. This information may be signaled using LPPasignaling.

In an example method, the serving eNB may inform the E-SMLC of the cellIDs of the inter-frequency cells, and optionally all cells, the WTRU maybe reporting measurements for. For example, this may include the cellIDs of the cells for which the WTRU is reporting RSRP and/or RSRQ. Thus,the E-SMLC is aware of the cells the WTRU is already hearing andmeasuring. This information may be signaled using LPPa signaling.

In an example method, the WTRU capability for inter-frequencymeasurements may be expanded to include RSTD measurements. For example,the WTRU may be required to be capable of performing RSRP, RSRQ, andRSTD measurements of at least 4 inter-frequency cells per frequencydivision duplex (FDD) inter-frequency carrier for up to 3 FDDinter-frequency carriers.

In an example method, the WTRU may have a requirement forinter-frequency RSTD measurements stating that the WTRU be capable ofperforming RSTD measurements of at least X inter-frequency cells per FDDinter-frequency carrier for up to Y FDD inter-frequency carriers. In oneexample, X=2 or 3 and Y=1 or 2. A similar requirement may be imposed fortime division duplex (TDD).

In an example, the WTRU may limit the number of inter-frequency cellsand/or carrier frequencies for which it makes RSTD measurements suchthat the total number of inter-frequency cells and carrier frequenciesfor which it makes any measurements does not exceed the capabilitiesrequired for RSRP and RSRQ.

For example, the WTRU may be capable of performing RSRP and RSRQmeasurements of at least 4 inter-frequency cells per FDD inter-frequencycarrier for up to 3 FDD inter-frequency carriers. If the WTRU, forexample, were making RSRP/RSRQ measurements on 3 inter-frequency cellsper FDD inter-frequency carrier for each of 2 FDD inter-frequencycarriers, then the capability requirement for RSTD would supportmeasurement on the cells already measured for RSRP/RSRQ plus anadditional 1 more cell on the existing 2 frequencies plus up to 4 cellson a 3^(rd) frequency.

Described herein is an example method that a WTRU 405 may follow usingthe methods described herein. The WTRU 405 may receive and storeconfigured inter-frequency measurement objects from the network 410(415). For example, an eNodeB or E-SMLC may send list(s) of measurementobjects to the WTRU 405 through RRC or LPP protocol message exchanges.Inter-frequency measurement objects may comprise carrier frequenciesother than the current serving cell frequency, or inter-frequency cellsincluding their respective identifiers. The WTRU 405 may then build thelist of valid positioning measurement objects based on either one ormore filtering criteria (420).

One filtering criteria may result in having some measurement objectsexcluded from the positioning candidate list. For example, a frequencynot also indicated by the eNB on the inter-frequency mobility list, maynot be usable by the WTRU 405 for positioning measurements. Otherfiltering criteria may result in one or more measurement objects beingprecluded from the list if signal strength or signal qualitymeasurements indicate low reliability. In yet another filtering criteriaexample, the list of measurement objects may be completed by includingcertain cells or frequencies not considered in the context ofinter-frequency measurements for other measurement purposes. Forexample, black-listed cells may be included for positioning purposes.

The WTRU 405 then stores the list of measurement objects for positioningpurposes (425) and starts executing positioning measurements accordingto a measurement schedule (430).

In addition to the initial building of the measurement object list, thesame or a different set of filter criteria may be used to refresh thelist of valid measurement objects for positioning purposes. This may bedone at update intervals. For example, reception of a new list ofinter-frequency channels may trigger an update to the measurement objectlist. Alternatively or additionally, a cell reaching sufficient signalstrength or signal quality may be included for positioning purposes.

Methods for determining which signals to measure for inter-frequencymeasurements are described herein. In one example method, only CRS maybe used for RSTD for inter-frequency cells. For example, while PRS andCRS both may be configured for the purpose of positioning measurementson the serving cell frequency, only CRS may be used on inter-frequencycells. In another method, the rules for choosing CRS versus PRS mayapply for both intra-frequency and inter-frequency cells.

Described herein are methods for determining how many subframes may beavailable for measurement accumulation. In one example method, thenumber of subframes available for accumulation (N_(PRS)) forinter-frequency PRS measurements may be different from the number ofsubframes available for accumulation for intra-frequency PRSmeasurements. For example, the number of subframes available foraccumulation (N_(PRS)) for inter-frequency PRS measurements may be lessthan the number of subframes available for accumulation forintra-frequency PRS measurements.

In an example method, the number of subframes available for accumulation(N_(PRS)) for inter-frequency PRS measurements may be signaled to theWTRU. For example, the number of subframes available for accumulation(N_(PRS)) for inter-frequency PRS measurements may be signaled to theWTRU as a separate parameter from the number of subframes available foraccumulation for intra-frequency PRS measurements.

In an example method, the number of subframes to use for accumulation(N_(PRS)) for inter-frequency PRS measurements may be a fixed number.For example, the number of subframes to use for accumulation (N_(PRS))for inter-frequency PRS measurements may be one subframe.

Described herein are methods for determining when to measureinter-frequency cells. In an example method, a network configuredmeasurement gap may be used for performing inter-frequency RSTDmeasurements. The rules for DL reception and UL transmission duringmeasurement gaps may apply. That is, during the measurement gap, theWTRU may not transmit any data and is not expected to tune its receiveron the E-UTRAN serving cell carrier frequency.

In another example method, the gap identified for inter-frequencyE-UTRAN measurements (for example RSRP and RSRQ measurements) may alsobe used for the inter-frequency RSTD measurements.

In another example method, a new measurement gap may be defined and usedfor the inter-frequency RSTD measurements. The gap length, the gapperiod, and the gap starting subframe may be provided to the WTRU by thenetwork. The gap parameters may be flexible enough to allow the patternsto overlay on the PRS patterns totally or in part. Additionally, theWTRU may not be required to make any UL transmissions during this gapsuch as sounding reference signal (SRS), acknowledgement/negativeacknowledgement (ACK/NACK), channel quality indicator (CQI) reports, andthe like. Additionally, the WTRU may not be expected to tune itsreceiver on the E-UTRAN serving cell carrier frequency during this gap.

In another example method, given N_(PRS) may be the number of subframesallocated for PRS, the WTRU may use some of the subframes forintra-frequency PRS measurements and some of the subframes forinter-frequency PRS measurements. For example, the WTRU may use the lastX subframes (or alternatively the first X subframes) of the N_(PRS)subframes to do the inter-frequency measurements. The value of X may beknown (fixed) or signaled to the WTRU. During the subframes used forinter-frequency measurements and any subframe(s) used for transitionbetween reception and/or operation on different carrier frequencies, theWTRU may not be required to make any UL transmissions, such as SRS,ACK/NACK, CQI reports, and the like. The WTRU may not be expected totune its receiver on the E-UTRAN serving cell carrier frequency duringthe subframe(s) used for inter-frequency measurements.

In another example method, cells transmitting with different carrierfrequencies may not transmit PRS in exactly the same subframes. Theallocations may partially overlap or not overlap at all. For purposes ofillustration only, consider cell1 transmitting with carrier frequency f1using allocation pattern 1 and cell2 transmitting with carrier frequencyf2 using allocation pattern 2. Allocation pattern 2 may be the same asallocation pattern 1, but shifted in time by a fixed number ofsubframes. In another illustration, allocation pattern 1 may be 4subframes every 16 frames beginning in subframe 0 of system frame number(SFN) 0 and allocation pattern 2 may be the same pattern, but beginningin subframe 4 of SFN 0. In this example, there would be 8 consecutivesubframes for PRS where the first 4 are for cells transmitting on f1 andthe second 4 are for cells transmitting on f2. In another example,allocation pattern 2 may be different from allocation pattern 1.

In this example method, the WTRU may be signaled the allocation patternsfor the inter-frequency cells. This may be on a cell basis or on acarrier frequency basis. During the subframes used for inter-frequencymeasurements and any subframe(s) used for transition between receptionand/or operation on different carrier frequencies, the WTRU may notrequired to make any UL transmissions, such as SRS, ACK/NACK, CQIreports, and the like. The WTRU may not be expected to tune its receiveron the E-UTRAN serving cell carrier frequency during the subframe(s)used for inter-frequency measurements.

In another example method, cells transmitting with different carrierfrequencies may not transmit PRS in exactly the same subframes. Thecarrier frequencies may be placed in groups and each group may have asubframe allocation defined. All cells with a carrier frequency in aparticular group may use the same subframe allocation.

In this example method, the WTRU may be told the allocation patterns forthe inter-frequency cells. This may be on a cell basis, on a carrierfrequency basis, or on a group basis. For the group basis case, a meansmay be provided for the WTRU to know which frequencies are in eachgroup. This may be fixed or signaled. During the subframes used forinter-frequency measurements and any subframes used for transitionbetween reception and/or operation on different carrier frequencies, theWTRU may not be required to make any UL transmissions, such as SRS,ACK/NACK, CQI reports, and the like. Additionally, the WTRU may not beexpected to tune its receiver on the E-UTRAN serving cell carrierfrequency during the subframe(s) used for inter-frequency measurements.

In another example method, the E-SMLC may provide information to theeNB(s) related to the configuration of WTRUs making inter-frequency PRSmeasurements such that the eNB(s) may be able to configure measurementgaps accordingly. This information may include the carrier frequenciesfor which the WTRU is being asked to make RSTD measurements. LPPasignaling may be used for this communication.

In another example method, the measurement gap to use forinter-frequency measurements may be implicitly configured by the PRSsubframe allocation, i.e., the network signaling the informationregarding the subframe allocation of the inter-frequency PRS signals tothe WTRU implies that a measurement gap is configured. The WTRU mayunderstand that this is a measurement gap and during this gap may not berequired to receive in the DL or transmit in the UL on the serving cell.

In an example method, cells transmitting with different carrierfrequencies may transmit PRS in the same subframes. The WTRU may be toldwhich period of the PRS allocation to use for intra-frequencymeasurements and which to use for inter-frequency measurements. Forexample, the WTRU may be told to use every Nth period of the PRSallocation for inter-frequency measurements, where N may be an integergreater than or equal to 1. The default value of N may be 1 and the WTRUmay not need to be informed by signaling if N is 1. Moreover, if N isalways 1, no additional signaling may be required to inform the WTRU.

In this example method, during the subframes used for inter-frequencymeasurements and any subframes used for transition between receptionand/or operation on different carrier frequencies, the WTRU may not berequired to make any UL transmissions, such as SRS, ACK/NACK, CQIreports, and the like. It is noted that during these subframesdesignated for inter-frequency PRS measurements, the WTRU may need totune its receiver to the serving (or other reference) cell carrierfrequency at the beginning of the period for some length of time (forexample, some number of subframes) to obtain the reference timing forthe measurements of the other cells. Except as stated above, the WTRUmay not be expected to tune its receiver on the E-UTRAN serving carrierfrequency during the subframe(s) used for inter-frequency measurements.

In one method, when the reference cell supports PRS, the OTDOAassistance data for the reference cell includes the PRS information forthe reference cell and the OTDOA assistance data for a neighbor cellincludes the PRS information for the neighbor cell if it is not the sameas the PRS information of the reference cell. PRS information mayinclude the PRS bandwidth, the PRS configuration index, where the PRSconfiguration index may be an index into a table which provides thesubframe allocation for the PRS (where the subframe allocationidentifies in which subframes PRS will be transmitted), and the like.

In the case where the reference cell supports PRS and a neighbor celldoes not, a means is needed to inform the WTRU that the neighbor doesnot support PRS. This may be done in one or more of the followingmethods. In one example method, in the PRS information for the neighborcell, the PRS bandwidth may be set to a specific value that isinterpreted by the WTRU to mean PRS is not supported in the neighborcell. For example, the PRS bandwidth may be set to a value that is not avalid PRS bandwidth value, which may, for example, be a value of allzeroes or all ones.

In another example method, in the PRS information for the neighbor cell,the PRS configuration index may be set to a specific value that isinterpreted by the WTRU to mean PRS is not supported in the neighborcell. For example, one of the reserved values may be used such as 4095.

In another example method, in the PRS information for the neighbor cell,specific values may be used for two or more of the parameters (thevalues may be the same or different for the different parameters) toindicate that PRS is not supported in the neighbor cell. For example,all the values may be set to 0. The WTRU may interpret the combinationof parameter values to mean that PRS is not supported in the neighborcell.

Although features and elements are described above in particularcombinations, one of ordinary skill in the art will appreciate that eachfeature or element can be used alone or in any combination with theother features and elements. In addition, the methods described hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable medium for execution by a computeror processor. Examples of computer-readable media include electronicsignals (transmitted over wired or wireless connections) andcomputer-readable storage media. Examples of computer-readable storagemedia include, but are not limited to, a read only memory (ROM), arandom access memory (RAM), a register, cache memory, semiconductormemory devices, magnetic media such as internal hard disks and removabledisks, magneto-optical media, and optical media such as CD-ROM disks,and digital versatile disks (DVDs). A processor in association withsoftware may be used to implement a radio frequency transceiver for usein a WTRU, UE, terminal, base station, RNC, or any host computer.

The invention claimed is:
 1. A method for supporting positioningmeasurements, comprising: designating a first cell as a reference cell;designating a second cell as a non-reference cell; and providing, via anetwork entity to a wireless transmit/receive unit (WTRU), referencecell information and non-reference cell information, wherein thenon-reference cell information includes: (1) a subframe offset between afirst Positioning Reference Signal (PRS) transmitted by the referencecell and a second PRS transmitted by the non-reference cell and (2) timedifference information indicative of a relative timing differencebetween the reference and non-reference cells based on the first andsecond PRSs.
 2. The method of claim 1, wherein the reference cell is anon-serving cell.
 3. The method of claim 1, wherein the non-referencecell information identifies a carrier frequency of the non-referencecell.
 4. The method of claim 1, wherein the reference cell informationincludes an identity of the reference cell.
 5. The method of claim 1,wherein the reference cell information includes PRS information for thereference cell on a condition that the reference cell supports PRStransmission.
 6. The method of claim 5, wherein the PRS informationincludes PRS subframe allocation information.
 7. A location server,comprising: a processor configured to: designate a first cell as areference cell; designate a second cell as a non-reference cell; andprovide reference cell information and non-reference cell information toa wireless transmit/receive unit (WTRU) for performing positioningmeasurements with respect to the reference cell and the non-referencecell, wherein the non-reference cell information includes: (1) asubframe offset between a first Positioning Reference Signal (PRS)transmitted by the reference cell and a second PRS transmitted by thenon-reference cell and (2) time difference information indicative of arelative timing difference between the reference and non-reference cellsbased on the first and second PRSs.
 8. The location server of claim 7,wherein the reference cell is a non-serving cell.
 9. The location serverof claim 7, wherein the non-reference cell information identifies acarrier frequency of the non-reference cell.
 10. The location server ofclaim 7, wherein the reference cell information includes an identity ofthe reference cell.
 11. The location server of claim 7, wherein thereference cell information includes PRS information for the referencecell on a condition that the reference cell supports PRS transmission.12. The location server of claim 11, wherein the PRS informationincludes PRS subframe allocation information.
 13. A method forsupporting positioning measurements, comprising: transmitting anidentity of a reference cell to a wireless transmit/receive unit (WTRU);transmitting, via a network entity to the WTRU, assistance data, whereinthe assistance data includes: (1) a subframe offset between a firstPositioning Reference Signal (PRS) transmitted by the reference cell anda second PRS transmitted by the non-reference cell, and (2) timedifference information indicative of a relative timing differencebetween the reference and non-reference cells based on the first andsecond PRSs; and receiving a measurement made using the assistance datafrom the WTRU.
 14. The method of claim 13, wherein the reference cell isa non-serving cell.
 15. The method of claim 13, wherein the assistancedata identifies a carrier frequency of the non-reference cell.
 16. Themethod of claim 13, wherein the assistance data includes an identity ofthe non-reference cell.
 17. A location server, comprising: a processorconfigured to: transmit an identity of a reference cell to a wirelesstransmit/receive unit (WTRU); transmit assistance data to the WTRU,wherein the assistance data includes: (1) a subframe offset between afirst Positioning Reference Signal (PRS) transmitted by the referencecell and a second PRS transmitted by the non-reference cell, and (2)time difference information indicative of a relative timing differencebetween the reference and non-reference cells based on the first andsecond PRSs; and receive a measurement made using the assistance datafrom the WTRU.
 18. The location server of claim 17, wherein thereference cell is a non-serving cell.
 19. The location server of claim17, wherein the assistance data identifies a carrier frequency of thenon-reference cell.
 20. The location server of claim 17, wherein theassistance data includes an identity of the non-reference cell.